Apparatus and method for virtual private telephone line with automatic ring down

ABSTRACT

Apparatus and method for establishing a virtual private line with automatic ring down is provided. The virtual private line uses the SS7 switching network of present telephone systems coupled between the customer premises equipment of two virtual private line customers.

TECHNICAL FIELD OF THE INVENTION

This invention relates in general to the field of telephony. More particularly, the present invention relates to apparatus and a method for virtual private telephone lines with automatic ring down.

BACKGROUND OF THE INVENTION

Dedicated private telephone lines between two parties have been established in the past by physically installing and maintaining a hard-wired telephone line connection between the parties. Facilities that are "manual ring down" requires the user to push a designated button on the telephone to ring the user on the other end of the hard-wired telephone line. The parties using a dedicated hard-wired telephone line with the "automatic ring down" feature may ring the other end of the line and establish a connection by simply raising the telephone handset or otherwise going "off-hook." Since the need to memorize and dial telephone numbers or even speed-dial numbers is obviated, the path of communication is established immediately. The private line service is typically favored by customers who make large volumes of calls from and to fixed locations and whose business requires continuous and uninterrupted lines of communication between those locations. A prime example of such a customer is a brokerage firm maintaining offices in Chicago and New York.

Needless to say, such dedicated hard-wired facilities are extremely expensive and difficult to install and maintain. Nevertheless, since such dedicated line service is demanded by certain telephone service subscribers, it has become desirable to provide a service that emulates a dedicated private telephone line but that does not require a physical hard-wire telephone connection. Accordingly, it has become desirable to use the existing telephone switching networks to establish private telephone line service. In particular, it is advantageous to use the rapid call setup ability of industry standard Signaling System 7 (SS7) to quickly establish private line calls with automatic ring down using the switched network.

SUMMARY OF THE INVENTION

In accordance with the present invention, apparatus and a method for a virtual private line with automatic ring down are provided which substantially eliminate or reduce disadvantages and problems associated with prior hot line or private line services.

In one aspect of the present invention, apparatus for a virtual private telephone connection between a User A telephone equipment and a User B telephone equipment is provided. The apparatus includes a first telephone switch coupled to the User A telephone equipment. The first telephone switch is capable for switching a plurality of trunk groups including at least one virtual private line trunk group. The virtual private line trunk group may include one or more trunk circuits. User B's telephone equipment is coupled to a second telephone switch which is also coupled to the first telephone switch. The second telephone switch is capable for switching a plurality of trunk groups including at least one virtual private line trunk group. Further included is a database which contains data for associating the virtual private line trunk group of the first switch with the virtual private line trunk group of the second switch. The apparatus also includes means for processing virtual private telephone connections between the User A and User B telephone equipment.

In another aspect of the present invention, a method for establishing a virtual private telephone line with automatic ring down between at least one User A telephone coupled to an originating trunk group and switch and at least one User B telephone coupled to a terminating trunk group and switch is provided. The originating switch is coupled to the terminating trunk group by an SS7 switched network. The steps include detecting User A telephone being off-hook and associating the originating trunk group coupled to User A telephone with the terminating switch and trunk group. User B's telephone is then alerted and User B's answering the call is detected. A virtual private line connection is then established between the User A telephone and the User B telephone.

An important technical advantage of the present invention is providing the benefits of a private line or an immediate hotline without the disadvantage of the physical hard-wiring. The virtual private line emulates a hard-wired private line by advantageously providing automatic ring down, end-to-end glare resolution, equitable billing arrangements based on originating usage, and other desirable features.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference may be made to the accompanying drawings, in which:

FIG. 1 is a greatly simplified high level block diagram of a preferred embodiment of the virtual private line circuit using an SS7 switch network;

FIG. 2 is a timing and signal flow diagram depicting a preferred embodiment of a normal call origination and setup scenario;

FIG. 3 is a timing and signal flow diagram depicting a preferred embodiment of a call suspend and resumption scenario;

FIG. 4 is a timing and signal flow diagram depicting a preferred embodiment of a normal call release scenario;

FIG. 5 is a timing and signal flow diagram depicting a preferred embodiment of a call expiration scenario with notification to the user remaining off-hook;

FIG. 6 is a timing and signal flow diagram depicting a preferred embodiment of processing of premature off-hook during release sequence; and

FIG. 7 is a timing and signal flow diagram depicting a preferred embodiment of an end-to-end glare resolution scenario.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawings, FIG. 1 illustrates a representative SS7 (Signaling System 7) telephone switch network diagram establishing a virtual private telephone line with automatic ring down, indicated generally at 10 and constructed according to the teaching of the present invention. The virtual private line is shown established between two subscribers, User A and User B. In general, subscribers at both ends of the virtual private line circuit use key telephone systems and the virtual private line is a "direct appearing line" on one or more user telephones.

As shown in FIG. 1, User A has dedicated three telephones 12-16 to this virtual private line, which are coupled to User A's customer premises equipment (CPE) telephone system 18. Customer premises equipment are equipment located on a customer's premises such as ISDN digital PBXs, non-ISDN digital PBXs, processor-controlled ISDN multiplexers, and processor-controlled bridges or routers. The customer premises equipment 18 is connected to a network switch X 22 via a Dedicated Access Line (DAL) 20. A representation of a database 21 is shown, which associates an incoming virtual private line trunk group with the Terminating Switch Identification number (TSID) and virtual private line Terminating Trunk Group (TTG) identification number. The telephone number or switch and trunk group identification provides the routing information for the virtual private line setup. Preferably, the database 21 is indexed by the incoming trunk group number and provides a 10-digit direct distance dialing (DDD) number or a 7-digit TSID+TTG pilot number as known in the telephony industry. Since SS7 is used, normal SS7 call processing procedures in addition to other processing methods are employed. Details of the virtual private telephone line processing is discussed below in conjunction with FIGS. 2-7.

Switch X 22 is shown coupled to a switch or a network of switches 25 and 26 via SS7 Inter Machine Trunk (IMT) connections 24. Switch(es) 22, 25, and 26 may represent Local Access and Transport Area and/or Inter Exchange Carrier switches. Switch(es) 25 is in turn connected to a Switch Y 26 which is coupled to User B's customer premises equipment (CPE) 30 via a dedicated access line (DAL) 28. As shown, Switch Y 26 also includes a database 27 containing routing information for the virtual private line. As shown, User B has three dedicated telephones 32-36 for the virtual private telephone service. Switches X 22 and Y 26 may be implemented by currently available switches such as the MegaHub 600E manufactured by DSC Communications Corporation of Plano, Tex., and the like. However, the virtual private line automatic ring down service implementation of the present invention preferably requires only a software modification and/or additions in the originating and terminating Switches X and Y. The details of the software modification and/or additions are discussed below in conjunction with FIGS. 2-7. As shown in FIG. 1, the virtual private line between Users A and B is arranged over three trunk circuits in a designated trunk group. However there is no upper limit for the number of trunk circuits that can be maintained in the virtual private line connection between two users.

A brief overview of the operations of virtual private line with automatic ring down would be beneficial. Initially, assume no telephones 12-16 and 32-36 are in use. If User A now picks up the handset of telephone 12, this fact is transmitted to Switch X 22 via CPE 18 and DAL 20. Switch X 22 recognizes that the trunk circuit used by telephone 12 belongs to a trunk group that has been designated as a virtual private line trunk group. Switch X 22 may maintain a database or table (not shown) that identifies a virtual private line trunk group by a trunk group number assigned to it. Switch X 22 then may access database 21 to determine the corresponding destination switch and virtual private line trunk group for User A.

Having determined that User B is the destination user for User A, Switch X 22 proceeds with the steps necessary to establish a connection with Switch Y 26 and User B. Since three telephones 32-36 are connected to the virtual private line, Switch Y 26 uses a trunk selection strategy or terminating circuit selection method to determine which telephone to ring. Such trunk circuit selection algorithms are widely used in the telephony industry, one of which can be studied by referring to, for example, LATA Switching Systems Generic Requirements--Tandem Supplement, Document no. TR-TSY-000540, issued in July, 1987 by Bell Communications Research. It is apparent from this discussion that the originating and terminating trunk groups of a virtual private line should contain the same number of trunks in order for all calls to complete. It is further apparent that the virtual private line of the present invention has an automatic ring down feature.

FIGS. 2-7 are timing and data flow diagrams showing preferred embodiments of various call processing scenarios. In these diagrams, the passage of time is represented in the vertical axis, while the data or messages are shown originating from specific hardware components and received by specific components corresponding to the network representation diagram shown in FIG. 1. An explanation of the acronyms used in the diagrams, specification and the claims is summarized in the table below. The SS7 messages generated by the switches 22, 25, and 26 are relayed or transmitted to the destination swithes by a signaling network represented by Signal Transfer Point (STP) 40 as know in the art. A detailed description of the various SS7 message formats and contents can be found in Chapters T1.113.1, T1.113.2, and T1,113.3-1992, Functional Description of the Integrated Services Digital Network (ISDN) User Part issued by American National Standard.

    ______________________________________                                         ACRONYMS AND TERMINOLOGY                                                       ______________________________________                                         ACM          SS7 Address Complete Message                                      ANM          Answer Message                                                    CPE          Customer Premises Equipment                                       DAL          Dedicated Access Line                                             DDD          Direct Distance Dialing Number                                    IAM          SS7 Initial Address Message                                       IMT          Inter Machine Trunk                                               REL          SS7 Release Message                                               RES          SS7 Resume Message                                                RLC          SS7 Release Complete Message                                      SUS          SS7 Suspend Message                                               SS7          Signaling System 7                                                VPL          Virtual Private Line                                              ______________________________________                                    

Referring to FIG. 2, a timing and signal flow diagram shows a preferred embodiment of a normal call origination and setup. Both User A and User B begin with their telephones on-hook, as indicated by the designation "IDLE" in the diagram. User A then went off-hook. In other words, User A raised the handset off the cradle of the phone, or otherwise turned the telephone on. When User A goes off-hook, Switch X recognizes a virtual private line request for service, and obtains special routing information such as a 7 or 10 digit number for identifying the terminating switch and trunk group. Switch X then initiates a call by sending an SS7 IAM message to the terminating switch or Switch Y in this instance. The IAM message contains the originating switch identification number and trunk group in the generic digits parameter in addition to other information as defined by the SS7 protocol. Switch Y receives the SS7 IAM message, alerts User B by ringing a selected one of his telephones, and returns an SS7 ACM message to Switch X. When User B picks up the telephone handset or goes off-hook, Switch Y is alerted and sends an SS7 ANM message to Switch X. In this manner, Switches X and Y establish a voice path and Users A and B converse.

Referring to FIG. 3, a preferred embodiment of call suspend and resume processing is shown. This is the scenario where the established connection is maintained when one of the users hangs up temporarily and then goes off-hook again. As shown initially, Users A and B are conversing via an established virtual private line connection. It is irrelevant in the preferred embodiment whether User A or User B initiated the call. As shown in FIG. 3, User A then hangs up or goes on-hook. In response to User A hanging up, Switch X issues an SS7 SUS message to Switch Y and starts the suspend timer 42. Switch Y also starts its suspend timer 44 in response to the SS7 SUS message from Switch X. The suspend timer is generally set to expire in approximately twenty to thirty seconds. As indicated in FIG. 3, User A then picks up the telephone again prior to the expiration of the suspend timer, which directs Switch X to send an SS7 RES message to Switch Y. The connection is then reestablished. It is worthwhile to note that User B, as the non-originating user, may also go on-hook temporarily and suspend the call and then have the ability to resume the call by going off-hook again as shown in FIG. 3.

Referring to FIG. 4, a normal call release scenario is shown. At the end of the conversation, User A first goes on-hook, which directed Switch X to send an SS7 SUS message to Switch Y and to also start the suspend timer. At approximately the same time or shortly thereafter, User B also goes on-hook, directing Switch Y to send an SS7 REL message to Switch X in response to Switch X's SUS message. Switch X then responds by cancelling the suspend timer and sending Switch Y an SS7 RLC message. This terminates the phone call and the connection is released. It can be seen that the same processing steps also apply if User B goes on-hook before User A in this scenario. The resulting timing diagram would merely be a mirror reflection of FIG. 4.

FIG. 5 illustrates the preferred processing of call expiration with notification to the user remaining off-hook. The diagram begins with Users A and B conversing via the established virtual private line connection. User A hangs up and goes on-hook, which directs Switch X to send an SS7 SUS message to Switch Y. Both Switches start the suspend timers. This time the suspend timers expire-before User A picks the phone-back up, so Switch X issues an SS7 REL message to Switch Y, and Switch Y cancels the suspend timer and responds with an SS7 RLC message. Switch Y then notifies. User B, who is still off-hook, with either a recorded voice message or an audible tone of a predetermined frequency and characteristics. This treatment alerts User B that User A has hung up and has not resumed the call so that User B should also hang up to terminate the call.

FIG. 6, shows the preferred method of processing a premature off-hook during a release sequence. This scenario occurs when both callers have hung up the phone having terminated a call, but one or both of them pick up the telephone handset too quickly before the release processing of the previous call has been completed. As shown in the diagram, User A goes on-hook at the end of the conversation, which prompts Switch X to issue an SS7 SUS message to Switch Y and to start the suspend timer. Switch Y also starts its suspend timer in response to the SS7 SUS message from Switch X. User B then goes on-hook also to terminate the call, which may precede or be simultaneous with User A's going off-hook again. Therefore, the SS7 RES message sent by Switch X, in response to User A's going off-hook and received subsequently to detecting User B's telephone being on-hook, is simply ignored by Switch Y. At the expiration of the suspend timer, Switch Y issues an SS7 REL message to Switch X. Switch X sends an SS7 RLC to Switch Y to signal the completion of the release. If User A remains off-hook, a new call is established in a manner identical to that described above and showed in FIG. 2.

In FIG. 7, the processing to resolve a special end-to-end glare situation is shown. End-to-end glare occurs when both User A and User B go off-hook simultaneously or nearly simultaneously. In a private line service using a physical hard-wired dedicated line, such occurrence simply produces an established connection between the subscribers to the private line. However, because the switched telephone network is used in the instant invention, when both users go off-hook an end-to-end glare situation is produced as both Switches X and Y attempt to set up the connection with each other. This situation is more common when only one trunk circuit is dedicated to a virtual private line trunk group, or when the multiple trunk circuits in the virtual private line trunk group are always busy so that only one trunk is generally free at any one time. The end-to-end glare is resolved in the following manner.

Referring to FIG. 7, both Users A and B pick up the telephone handset substantially simultaneously. This is conveyed to the respective Switches X and Y, each of which sends an SS7 IAM message to each other in an attempt to initialize call setup. To differentiate the IAMs, they are designated as #1 and #2, sent by Switch X and Switch Y, respectively. When Switch X receives the IAM #2 message from Switch Y and Switch Y receives the IAM #1 message from Switch X, both Switches realize that an end-to-end glare situation is occurring. Each switch then independently compares its own switch identification number with the identification number of the other switch. The Switch with the lower switch identification number is given permission to proceed as the originating switch in call setup, and the other switch backs down. If the switch identification numbers are the same, then trunk group identification numbers of the respective virtual private line trunk groups are compared, and the switch with the lower virtual private line trunk group identification number proceeds as the originating switch. For example, assume that Switch X has a lower switch or trunk group identification number, therefore Switch Y backs down and Switch X proceeds. Switch X issues an SS7 REL message with a predetermined cause code to Switch Y indicating that the switch associated with IAM #2 is to back down, and the switch associated with IAM #1 is to proceed. Thereafter, Switch Y sends an SS7 ACM and ANM messages to Switch X, generally following the normal call setup procedure shown in FIG. 2. The call origination from User B will proceed from Switch Y to Switch X in the manner generally following the normal call setup as in FIG. 2. In this manner, end-to-end glare is resolved and connection between Users A and B is established.

Implemented in the manner discussed above, a virtual private line with automatic ring down is provided which advantageously uses existing SS7 based telephone switching networks. Where not specifically discussed, standard SS7 processing applies. Although SS7 has been specifically identified and described in conjunction with the virtual private line, it is contemplated that other switching protocols and networks may be similarly adapted for the implementation of the virtual private line with automatic ring down. Furthermore, although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made thereto without departing from the spirit and scope of the present invention as defined by the appended claims. 

What is claimed is:
 1. Apparatus for a virtual private telephone connection between a User A telephone equipment and a User B telephone equipment, comprising:a first telephone switch coupled to said User A telephone equipment, said first telephone switch capable for switching a plurality of trunk groups including at least one virtual private line trunk group, said at least one virtual private line trunk group including one or more trunk circuit; a second telephone switch coupled to said first telephone switch and further coupled to said User B telephone equipment, said second telephone switch capable for switching a plurality of trunk groups including at least one virtual private line trunk group, said at least one virtual private line trunk group including one or more trunk circuit; a database accessible by said first and second telephone switches, said database being capable of associating said virtual private line trunk group of said first switch with said virtual private line trunk group of said second switch; said first and second telephone switches processing virtual private telephone connections between said User A and User B telephone equipment; means coupled to said User A telephone equipment for detecting said User A telephone being on-hook; means for transmitting an SS7 Suspend message to said second telephone switch in response to said User A telephone being on-hook; a suspend timer residing in said first telephone switch for beginning timing in response to said User A telephone being on-hook, said suspend timer expiring after a predetermined amount of time; means for detecting said User A telephone being off-hook prior to the expiration of said suspend timer and alerting said first switch accordingly; and means residing in said first telephone switch for transmitting an SS7 Resume message to said second telephone switch in response to the alert from said detecting means and reestablishing the virtual private line connection.
 2. The apparatus, as set forth in claim 1, further comprising:means coupled to said User A telephone equipment for detecting said User A telephone being on-hook; means for transmitting an SS7 Suspend message to said second telephone switch in response to said User A telephone being on-hook; a suspend timer coupled to said first switch for beginning timing in response to said User A telephone being on-hook, said suspend timer expiring after a predetermined amount of time; means for transmitting an SS7 Release message to said second telephone switch in response to the expiration of said suspend timer; means for transmitting an SS7 Release Complete Message to said first telephone switch in response to receiving said SS7 Release Message; and means for alerting User B with a predetermined treatment.
 3. The apparatus, as set forth in claim 1, further comprising:means coupled to said User A telephone equipment for detecting said User A telephone being on-hook; means for transmitting an SS7 Suspend message to said second telephone switch in response to said User A telephone being on-hook; a suspend timer residing in each of said first and second telephone switches for keeping the time said User A telephone being on-hook and expiring within a predetermined amount of time; means residing in said second telephone switch for detecting said User B telephone being on-hook prior to the expiration of said suspend timer in said second telephone switch; means for detecting said User A telephone being off-hook again prior to the expiration of said suspend timer in said first telephone switch; means for transmitting an SS7 Resume Message to said second telephone switch in response to detecting said User A telephone being off-hook prior to the expiration of said suspend timer; means for transmitting an SS7 Release Message to said first telephone switch in response to detecting said User B telephone being on-hook prior to receiving said SS7 Resume Message from said first telephone switch; means for alerting User A with a predetermined treatment in response to receiving said SS7 Release Message from said second telephone switch; and means for transmitting an SS7 Release Complete Message to said second telephone switch.
 4. A method for establishing a virtual private telephone line with automatic ring down between at least one User A telephone coupled to an originating virtual private line (VPL) trunk group and an originating telephone switch and at least one user B telephone coupled to a terminating virtual private line trunk group and terminating telephone switch, where the originating switch is coupled to the terminating trunk group by an SS7 switched network, the method comprising the steps of:detecting at least one User A telephone being off-hook; associating the originating VPL trunk group coupled to said at least one User A telephone with the terminating switch and VPL trunk group; ringing at least one user B telephone; detecting at least one User B telephone in response to the ringing being off-hook; establishing a virtual private line connection between the off-hook User A telephone and the off-hook User B telephone; after establishing the VPL connection, detecting the off-hook User A telephone being on-hook; transmitting an SS7 Suspend message from said originating switch to said terminating switch; starting a suspend timer said suspend time due to expire within a predetermined amount of time; detecting the User A telephone being off-hook prior to the expiration of said suspend timer; transmitting an SS7 Resume message from said originating switch to said terminating switch; and reestablishing the virtual private line connection.
 5. The method, as set forth in claim 4, further comprising the steps of:detecting User A telephone being off-hook and detecting User B telephone being off-hook substantially simultaneously; transmitting an SS7 Initial Address Message from the originating switch to the terminating switch; transmitting another SS7 Initial Address Message from the terminating switch to the originating switch; comparing a switch identification number of the originating switch with a switch identification number of the terminating switch; comparing a trunk group identification number of the originating trunk group with a trunk group identification number of the terminating trunk group in response to the switch identification numbers being identical; transmitting an SS7 Release Message from the switch with the lower switch or trunk group identification number to the switch with the higher switch or trunk group identification number; transmitting an SS7 Address Complete Message from the switch with the higher switch or trunk group identification number to the switch with the lower switch or trunk group identification number in response to the SS7 Release Message; transmitting an SS7 Answer Message from the switch with the higher switch or trunk group identification number to the switch with the lower switch or trunk group identification number; and establishing the virtual private line connection.
 6. The method, as set forth in claim 4, further comprising the steps of:after establishing the VPL connection, detecting User A telephone being on-hook; transmitting an SS7 Suspend message from said originating switch to said terminating switch; starting a suspend timer due to expire within a predetermined amount of time; transmitting an SS7 Release message from said originating switch to said terminating switch in response to the expiration of said suspend timer; transmitting an SS7 Release Complete Message from said terminating switch to said originating switch in response to receiving said SS7 Release Message; and alerting User B with a predetermined treatment.
 7. The method, as set forth in claim 4, further comprising the steps of:after establishing the VPL connection, detecting User A telephone being on-hook; transmitting an SS7 Suspend message from said originating switch to said terminating switch; starting a suspend timer due to expire within a predetermined amount of time; detecting User B telephone being on-hook prior to the expiration of said suspend timer; detecting User A telephone being off-hook again prior to the expiration of said suspend timer; transmitting an SS7 Resume Message from the originating switch to the terminating switch in response to detecting said User A telephone being off-hook prior to the expiration of said suspend timer; transmitting an SS7 Release Message from said terminating switch to said originating switch in response to detecting said User B telephone being on-hook prior to receiving said SS7 Resume Message; alerting User A with a predetermined treatment in response to receiving said SS7 Release Message; and transmitting an SS7 Release Complete Message from said originating switch to said terminating switch.
 8. The method, as set forth in claim 4, wherein said step of associating the originating trunk group coupled to User A telephone with the terminating switch and trunk group comprises the steps of:maintaining a database establishing a one-to-one correspondence between originating and terminating switches and virtual private lines trunk groups; and indexing with an originating trunk group identification number and accessing the corresponding terminating switch and trunk group identification numbers in said database.
 9. A method for resolving end-to-end glare in a virtual private line between a first and second telephones coupled to first and second switches, respectively, comprising the steps of:detecting said first and second telephones being off-hook substantially simultaneously; said first switch transmitting a call initiation message containing its identification number to said second switch; said second switch transmitting a call initiation message containing its identification number to said first switch; said first and second switches independently comparing the identification numbers and determining one of said first and second telephones as a call originator and the other as a call terminator based on said comparison of said identification numbers; said call originator transmitting a message to said call terminator to back down; and setting up said virtual private line connection. 